Economical desalination processes in Qatar

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Author

Al-Thani, Faleh N

Attention

2299/14043

Abstract

The limited underground water resources and the dramatic increase of fresh water
consumption in Qatar forced the government to seek alternative ways to compensate
for the lack of fresh water resources. Unfortunately, most of the currently available
alternatives are costly in terms of excessive fuel consumption; also they require large
capital investment and high maintenance cost. Such plants currently produce over
98% of the total fresh water in Qatar. This ratio may increase to 100% in the next few
years. The main aim of this work is to investigate the most viable water desalination
processes, which can produce sufficient, and a continuous supply of fresh water with
low operation and construction costs.
Climatic conditions and solar radiation in Qatar have been studied and analysed to
determine the performance of any potential solar system applicable to this country. A
technical and economical investigation into the current and common desalination
methods with particular emphasis on the three main desalination systems including
multistage flash, multiple effect distillation and reverse osmosis were conducted and
included. A comprehensive literature survey on various water desalination methods
was undertaken.
The current experimental program was confined mainly to one novel type of tilted
tray solar still system, namely pyramid tilted tray solar still, which was developed to
increase productivity by increasing the receiving surface area of the still (the
absorber) in order to collect the optimum amount of solar radiation. Two types of
cover have also been selected and tested in this work, namely pyramid and dome
shapes. These tilted tray solar stills were designed and constructed on a small scale
and have been tested under controlled laboratory conditions at the University of
Hertfordshire. Various parameters, which are likely to effect the still performance
have been investigated. These include water flow rate, spacing between cover and tray
surface, glass thickness, insulation layer, and inlet water temperature. Finally, a
comparison of the stills performance characteristics of the two shapes has been carried
out. The laboratory experimental results of hourly production revealed that pyramid
type solar still yield higher distilled water output results than the dome type.
However, the use of the pyramid shape with tilted tray solar can lead to further
increase in the still productivity by optimising the orientation and surface area of the
still absorber.
The field experimental results of pyramid solar still, which were conducted under
local climate conditions of Qatar, indicated clearly that solar desalination can be a
suitable economical option, particularly for remote areas, where the fresh water
demand is low and water transport is expensive. Moreover, a theoretical model was
employed to predict the effects on solar still performance under three various
parameters under typical climatic conditions of Qatar; These include the thermal
insulation layer, the water depth and wind speed. Due to the economical reasons the
dual-purpose multistage flash process will remain for the foreseeable future the
preferred process, when fresh water and electricity demands are growing concurrently
and rapidly.